In recent years, with the continuous increase of Internet access requirements for intelligent terminals, a cellular network can hardly satisfy bandwidth resources required by various services. With the increase of accordingly emerging multi-mode terminals, such as dual-mode terminals that support a cellular network and a wireless local area network (Wireless Local Area Network, WLAN), using a WLAN to offload traffic on a cellular network becomes a trend in the industry.
Offload (offload) refers to smoothly migrating a mobile data service from one network to another network. In order to use a WLAN to perform offload for a cellular network, the 3rd Generation Partnership Project (3rd Generation Partnership Project, 3GPP) puts forward an access network discovery and selection function (Access Network Discovery and Selection Function, ANDSF) to assist a terminal in selecting an access network. Specifically, the ANDSF server and the terminal both support the Open Mobile Alliance (Open Mobile Alliance, OMA) Device Management (Device Management, DM) protocol. An ANDSF server and a terminal that are located on a core network of a cellular network communicate by using the S14 interface, so that the terminal obtains a network selection policy. For example, the terminal uses a push (push) manner, that is, it passively receives a network selection policy sent by the ANDSF server, or uses a pull (pull) manner, that is, the terminal proactively queries the ANDSF about the network selection policy. Then, according to the obtained network selection policy, the terminal discovers and selects the access network on its own.
In addition, using a WLAN to perform offload for a cellular network may also be implemented by using related mechanisms defined by the Institute of Electrical and Electronics Engineers (Institute of Electrical and Electronics Engineers, IEEE). Specifically, the terminal acquires related information of a WLAN, a 3G network, and the like. For example, the terminal proactively sends a probe request (Probe Request) frame to an access device of the WLAN; or passively receives a beacon (Beacon) sent by an access device of the WLAN so as to obtain related information of the WLAN. Then, according to the obtained network information, the terminal discovers and selects the access network on its own.
However, in both the foregoing offload methods, the terminal discovers and selects the access network on its own, so that a network side can hardly accomplish a full control of the offload action of the terminal.